21. Go to/host theme parties. Once people age out of their 20s, no one’s trying to wear pajamas or Saran Wrap out of the house. The only theme parties that exist after your 20s are ‘Wedding,’ ‘Baby Shower,’ and ‘Funeral.’

My general advice for your 20's would be to leverage assets generally unique to that time of life: your remaining physical prime, higher adaptability and tolerance for new environments and ideas, and the freedom that comes from not having a family yet. It's a time to cultivate and enjoy option value, and also to maximize your exposure to as broad a set of people, places, and ideas as possible, if for nothing else than to know what the world has to offer before option value starts to lessen in value in your life, and you start to trade it for certainty.

I had a 30 before 30 list, and while I didn't check everything off the list, it was useful to have one. Of items on the list, I'd highly recommend:

Travel to all 7 continents. I missed Antarctica, but the goal forced me to travel on a regular schedule. The easiest way to expand your worldview and reduce your tendency to reductivist "us vs. them" mentality is to become a citizen of the world. When speaking with people in that country, your first resort should be their native language.

Live in New York City. No more efficient place in the U.S. to meet as many people as quickly, and as such, the ideal place to develop your socialization skills (making friends, dating, everything in between). As an expensive place to live, it teaches you to both hustle and live with less (space, money, material possessions) quickly. The wealth of options and opportunity eventually force you to find your own compass to avoid being overwhelmed or lost.

Don't live in New York City. Learning to find your equilibrium in a new place teaches you how much of your own happiness is intrinsic rather than environmental.

Run a marathon. Or something physically so challenging you have to train for months on end to even have a chance of finishing, like climbing a mountain, or biking 200 miles in a day. Finding your physical limits is useful hardening of the soul. It teaches you to structure your efforts over extended period of time, and the time required often forces you to be more disciplined in scheduling the rest of your life. Making it something you need to train a long period just to finish keeps you from cheating, one advantage of physical challenges.

Pick up one new skill a year. Playing the piano. Scuba diving. Learning to cook. Getting your pilot's license. Photography. Learning Photoshop. Something new every year. It's important to maintain the educational pace from your college days, just to turn it into habit. With the advent of so many online courses, now, it's easier than ever.

If you believe the adage that the paths not taken are the ones you regret later in life, then the best way to mitigate that early in life is to take as many different paths as possible. Fear and discomfort seemed to be more useful guides as to what to seek out in my 20's. As you age, you fear less and tend to avoid discomfort.